The design of vacuum glazing involves a complex set of trade offs between thermal performance and stress. In particular, the support pillars serve to concentrate the forces due to atmospheric pressure, leading to high levels of stress in the glass in the immediate vicinity of the support pillars. Such stresses can lead to local fractures of the glass. Further, the glass sheets bend over the support pillars giving rise to regions of tensile stress on the external surfaces of the glass sheets immediately above the support pillars. In addition, the pillars themselves experience high levels of stress, and must be made out of a material which has a very high compressive strength. Finally, the support pillars themselves act as thermal bridges between the glass sheets, leading to heat flow through the glazing.
Substantial progress has been made in the design and manufacture of vacuum glazing over the last few years. Vacuum glazings up to 1 m.times.1 m have been produced with high levels of thermal insulation. It has been shown that reasonable design compromises can be achieved between the competing constraints associated with mechanical tensile stress on the one hand, and heat flow through the glazing on the other.